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Vision isn't always WYSIWYG: Interactive optical illusions

by

Gianni A. Sarcone

Sunday, June 1, 2003

In English there are 2 essential words to express the faculty and the act of seeing: 1) see, 2) view. The etymological sense of the words see and view are "follow something with the eyes" (from the indo-European seq) and "have learnt" (from the indo-European weid). So, for our ancestors an image is something to shape with the eyes (follow with the eye) and information taken from the real world (having learnt from this visual perception).

Unfortunately (or fortunately?), seeing isn't some kind of direct perception of reality. Actually our brain is constantly interpreting and giving structure to the initial visual input from our eyes. If this was not the case, we wouldn't see colors and we probably would see the world upside down!

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Another interesting everyday paradox of our vision is that we don't see the edges of our visual field! In fact, we should see black zones outside of our visual field, but our brain cancels out these zones with a smooth fade-out effect. Below we have included some new optical illusions for you to experiment with...

Experiment 1: Concentric Objects

Some regular concentric objects appear to rotate when we approach or move back from them while staring at the center of the whole image:

Stare at the center of the geometric picture above, keeping your gaze fixed on the center. Move your head backwards and forwards. The rings will appear to rotate in opposite directions! This kind of effect must be related to how fast our eyes can focus and adjust for proximity (delay of readaptation) during each pendulum-swing of the head.

Experiment 2: Blinking Dot

Try now to focus for a while on the blinking dot at the center of the moving pattern below, by doing this you'll make the 3 dark blue dots vanish (singly, in pairs or all three). Steady vision induce disappearance, gaze shifts induce reappearance.

Experiment 3: Size of the Moon

Psychologically, we tend to see objects larger (or smaller) than they are in reality. Could you say what is the actual size of the moon? Is it as large as 1, 0.05 or 0.01 euro? You might be surprised to learn that in fact the moon is as large as 0.01 euro (or a US dime) seen at a distance of 2 meters! You can verify it...

About the author

Gianni A. Sarcone and Marie J. Waeber, designers and writers, are specialists in creative learning. They create and invent educational manipulative and thinking games which help teach mathematics, visual and plastic arts. Their maxim is: "be curious first!".